Skink city Families of reptilian master builders are working together to construct elaborate systems of tunnels in the central Australian desert, the first example of cooperative behaviour in reptiles, say Australian researchers.

The researchers, from Macquarie University in Sydney, working with indigenous communities, discovered the tunnel complexes in the sandy spinifex plains surrounding Uluru.

Built by great desert burrowing skinks (Liopholis kintorei), the labyrinthine tunnel networks can be up to 13 metres wide and a metre deep, with dozens of interconnecting passages. Each network has as many as 20 entrances, including several narrow 'pop' holes created by juveniles and latrines where the burrow residents defecate.

Dr Adam Stow of Macquarie University, who conducted the research along with Steve McAlpin and Paul Druckett, says tunnel building is a real preoccupation for skinks of all ages, requiring constant maintenance during the active season.

"They dig out the dirt with their forelimbs and slowly drag it backwards to a nearby entrance then kick it several feet away," says Stow.

The researchers found each skink city may be continuously occupied for up to seven years.

A first for lizards

While building a home to protect juveniles is common in many vertebrates, it was previously unknown in lizards.

A few other related skink species are known to live in family groups, but these are often forced to do so because of the habitat they live in: if there is only one rocky outcrop in the area and they depend on it for shelter, they have little choice but to live together.

Burrowing skinks live in an open environment and need to build their own homes to protect their offspring against predators and the elements.

Previous research has shown adult burrowing skinks form long-term pair bonds, breeding annually and giving birth to a cohort of between one and seven live offspring at a time.

Stow and colleagues genetically analysed tissue samples from the skinks, along with the latrine contents to determine parentage and social structure among a burrow's inhabitants. They found that adult pairs share their burrows with up to three cohorts of offspring at a time.

"These lizards are particularly unusual because they are constructing a long-term home for their offspring, and also because multiple individuals are cooperating in the burrow's development," he says. "This is unique among more than 5000 lizard species."

Stow says the burrows are built in close proximity to underground termite colonies, one of the skinks' favourite foods.

"As well as easy access to food, the tunnels provide shelter that is less prone to desert temperature extremes, and may help the residents maintain optimal body temperatures for longer periods," he says.

"For adults to invest so much in a home within which kids mature, it makes evolutionary sense that these adult individuals are sure that they are providing for their own offspring.

"In a broader sense it is also interesting because researchers believe that a level of relatedness is required in order for cooperative behaviour to develop among any group of animals," he added. "These lizards provide an independent example of that evolution."

Endangered species

Herpetologist and skink expert Dr Glenn Shea from the University of Sydney agrees with the researchers finding.

"There is an old-fashioned tendency to think of reptiles as inferior members of the vertebrate world, of not having a social life and of having little interest in their offspring," says Shea.

"This is one of very few examples of reptiles showing the same level of social interaction as birds and mammals.

Shea says the skink is currently listed as endangered, further increasing the need to understanding its behaviour.

"It is important that we know about their biology in order to develop appropriate conservation and management techniques."